1. Field of the Invention
The present invention relates to a backlight unit having a color adjusting function and a liquid crystal display device having backlight units.
2. Description of the Prior Art
The liquid crystal display device has such a merit that the device is thin in thickness, is light in weight, is driven by a low voltage, and needs small power consumption. Thus, the liquid crystal display device is extensively employed in various electronic devices.
In particular, the active-matrix type liquid crystal display device in which active elements such as TFTs (Thin Film Transistors) are provided every pixel is excellent such that the device is equivalent to the CRT (Cathode-Ray Tube) in the respects such as the luminance, the viewing angle characteristic, etc. Therefore, recently the liquid crystal display device of this type is also employed as the display device for the mobile television, the personal computer, etc.
Normally the backlight units are incorporated into the liquid crystal display device on the back surface side of the liquid crystal display panel. The transmittance of lights that are emitted from the backlight units is controlled every pixel constituting the liquid crystal display panel to display the image.
FIG. 1 is a sectional view showing a configuration of the liquid crystal display device including the backlight unit in the prior art.
The backlight unit has a light guide plate 61, white color fluorescent tubes 63 arranged on both longitudinal sides of the light guide plate 61 respectively, and reflectors 62 for reflecting the lights that are emitted from these fluorescent tubes 63 toward the light guide plate 61 respectively. The backlight unit is installed in a casing 69. A reflection sheet 66 is arranged on the back surface side of the light guide plate 61, and a diffusion sheet 64 and a prism sheet 65 are laminated to be arranged on the front surface side.
A liquid crystal panel 67 is placed over the prism sheet 65, and is fitted to the casing 69 by using a metal bezel 68.
In the liquid crystal display device constructed in this manner, the lights emitted from the fluorescent tubes 63 enter into the light guide plate 61 directly or after they are reflected by the reflectors 62. The incident lights into the light guide plate 61 can propagate through the light guide plate 61 while reflecting repeatedly between an upper surface and a lower surface of the light guide plate 61. The lights that exceed a critical angle are emitted from the light guide plate 61 to the liquid crystal panel 67. The lights that are emitted from the light guide plate 61 are diffused by the diffusion sheet 64 and the prism sheet 65 such that the direction of the light is regulated, and then reach the liquid crystal panel 67.
It is an object of the present invention to provide a backlight unit having a color adjusting function to itself and a liquid crystal display device having backlight units.
In order to achieve the above object, there is provided a backlight unit of the present invention comprising a plurality of light sources whose luminescent chromaticities are different mutually, said plurality of light sources including at least one white color light source; and a light guide plate for receiving lights emitted from said plurality of light sources and emitting the lights to a predetermined direction.
According to the above configuration, in the backlight unit of the present invention, a plurality of light sources whose luminescent chromaticities are different mutually are provided to give a color adjusting function to the unit itself, and the luminances of respective light sources are controlled independently by the control voltages supplied from external devices. For example, since the white color fluorescent tube, the red color fluorescent tube, the green color fluorescent tube, and the blue color fluorescent tube are provided as the light sources, the lights emitted from the light guide plate can be controlled into the desired color.
In this case, since the white color fluorescent tube is provided, the magnitude of the influence upon the luminance change and the color change caused when a quantity of the lights emitted from the red color fluorescent tube, the green color fluorescent tube, and the blue color fluorescent tube are changed independently can be relaxed and adjusted by the luminance level of the white color fluorescent tube.
Such backlight unit is arranged on the back surface side of the liquid crystal panel, and the liquid crystal display device that is able to display the image having the excellent color reproducibility can be obtained.